The invention relates to a television pickup arrangement having a solid state pickup device. The pickup device has a picture pickup portion, a field memory portion coupled to the pickup portion and a parallel-in series-out output shift register coupled to the field memory portion for producing a picture signal at a register output. The pickup arrangement also includes a clock signal circuit for controlling the picture pickup device according to a field transfer system, and a correction arrangement for reducing signal smear which is produced when the signal is transferred from the picture pickup portion to the field memory portion.
The correction arrangement has a memory device. This memory device is repeatedly readable with a repetition period equal to a television line period. The memory device stores a smear picture signal to be applied once during every television field period in a field blanking period via a changeover switch. The smear picture signal comprises signal smear information received from under an opaque strip provided on the picture pickup portion. The correction arrangement also includes a signal combining circuit having two inputs and an output. The inputs are coupled to the output of the output shift register and to the memory device, respectively. The output of the combining circuit is intended to supply the corrected picture signal at an output terminal of the pickup arrangement.
Such a television pickup arrangement is disclosed in U.S. Pat. No. 4,010,319. The signal smear is corrected by subtracting (in the signal combining circuit) the smear picture signal, containing smear information received from under the opaque strip provided on the pickup portion, from the picture signal corresponding to the scene image on the picture pickup portion. This signal subtraction operation is performed with one specific smear picture signal for every line scanned in a field scanning period.
The correction arrangement for reducing the signal smear is most effective when no moving portions are present in the scene to be televised or if there is only movement in the scene is in a direction which corresponds to the direction of the signal transfer from the picture pickup portion to the field memory portion. This signal transfer direction is transverse to the television line scanning or horizontal direction and consequently is in the vertical (field scanning) direction. It has been found that in practice when the known correction arrangement is used, there is still an annoying signal smear still occurs on display of the picture signal if one or more bright portions are present in the scene moving in the direction of line scan or in the opposite direction, that is to say in the horizontal direction.